“The subjective test 25. It is clear that before an officer makes a discovery assessment, he must have formed a certain state of mind. The question raised on this appeal is: what must the officer think or believe? The three judges in the Divisional Court in R v Kensington Income Tax Commissioners all agreed that it was not necessary for the officer to reach a conclusion which was justified by sufficient legal evidence. However, when describing what was required for this purpose, the three judges expressed themselves in different terms which do not appear to us to describe the same test. 26. Any test which is devised as to the necessary subjective belief on the part of the officer must be a practical and workable test. The expression of the test has to recognise that at the time when an officer thinks that it is desirable to make a discovery assessment, the officer may appreciate that in certain respects he may not be in possession of all of the relevant facts. Further, the officer may foresee that a discovery assessment might give rise to questions of law some of which might not be straightforward. 27. In Revenue and Customs Commissioners v Lansdowne Partners Ltd Partnership, when considering the meaning of “be aware of” for the purposes of s 29(5), it was said that “awareness” was a matter of perception not conclusion and that it was possible to say that an officer was “aware of” something even when he could not at that stage resolve points of law and even though he was not then aware of all of the facts which might turn out to be relevant. Although the word “discover” and the phrase “be aware of” cannot be treated as synonyms, we consider that if it is possible to be aware of something when one does not know all of the relevant facts and one cannot foretell how relevant points of law will be resolved, it cannot be said to be premature for an officer to “discover” that same something even when he knows he is not in possession of all of the relevant facts and does not know how relevant points of law will be resolved. 28. In Sanderson, Patten LJ described the power under section 29(1) in this way: “The exercise of the section 29(1) power is made by a real officer who is required to come to a conclusion about a possible insufficiency based on all the available information at the time when the discovery assessment is made”
“The officer must believe that the information available to him points in the direction of there being an insufficiency of tax”